6. Read the text and find following equivalents of word expressions:
Information ground
Work To help
To maintain direction Natural resources
Quality
Lesson 5
1. Read and memorize the words:
dial -
to plot
traverse , ,
draft ,
grid ,
needle -
jeweled cap ,
arm -
inclination -
foresight
backsight
tripod ,
screw -
clamp -
socket joint
to level
Read and translate the text
The Miners Dial And Its Use
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It is not always convenient or practical and underground it is rarely possible to conduct surveys so that they can be plotted from the lengths of the survey lines alone. In the method of surveying known as traversing the directions of the survey lines are fixed by angular measurements while their lengths and offsets from them are measured just as in chain surveying. Thus in Fig.1 AB, BC, CD represent three lines or drafts of a traverse. An instrument is used to measure either the angle which the line makes with some standard direction ά1 and ά2 or to measure the angle θ between two adjacent lines of the traverse, e.g. BC and CD. In the former case these angles or bearings are obtained directly in the field, the standard direction being either magnetic, geographic or grid north or some selected direction such as the first line of the traverse.
The miners dial has been extensively used in order to measure directly the bearings of underground traverse lines, and has been considerably improved in recent years. The original simple form consists of a circular compass plate divided into single degrees and read against the north end of a finely pointed needle mounted on a jeweled cap. The compass plate is extended in the N S directions by strong arms that carry a pair if sights, so arranged that a slit and a hair in an opposite window constitute a line of sight in either direction N or S and over a wide range of inclination. In a correctly adjusted instrument the plane of the two sights foresight and backsight are coincident. The compass box is mounted on a conical or cylindrical bearing so that it is free to move in azimuth and is clamped to the head of a tripod by a screw, while a ball and socket joint permit the instrument to be leveled. With such an instrument the sights and graduated circle move round the freely pivoted and more or less stationary compass needle.
3. Answer the following questions:
1. How are the survey lines fixed in the method of traversing?
2. What do the lines AB, BC, DC in Fig. 1 represent?
3. What instrument is used to measure the angles?
4. What is the miners dial used for?
4. Describe the principle of operation of miners dial.
